The present invention relates to self-bonding silicone rubber compositions and more particularly the present invention relates to SiH-olefin platinum catalyzed self-bonding silicone rubber compositions in which the self-bonding additive is the partial hydrolysis product of an aliphatically unsaturated hydrolyzable alkoxy silane.
SiH-olefin platinum catalyzed compositions are well known. Such compositions generally comprise a vinyl-containing polysiloxane polymer as the base polymer, a filler which may be a reinforcing filler such as fumed silica or precipitated silica, or an extending filler such as fused quartz incorporated into the base vinyl containing polymer. Also, a vinyl containing silicone resin may be used with or in place of reinforcing fillers. Such a mixture is generally stored separately. The cross-linking portion of the composition comprises a hydride siloxane which may either be a hydride-containing polysiloxane or hydride containing silicone resin. A platinum catalyst is used to promote the cure. Various other ingredients may be added to the composition so as to enhance its cured physical properties such as, for instance, there may be added to the composition low viscosity vinyl-containing polymers. The platinum catalyst may either be incorporated with the base vinyl-containing polymer and filler or it may be packaged with the hydride siloxane cross-linking agent. When it is desired to cure the composition, the two packages or two components are mixed together and the composition is applied in the desired manner and cures at room temperature or at higher temperatures to form a silicone elastomer.
There may also be incorporated into such compositions well known inhibitors such as, for instance, acetylenic compounds and other types of compounds which inhibit the cure of the composition at room temperature. When such an inhibited composition is heated at elevated temperatures, that is temperatures above 100.degree. C., the effect of the inhibitor is destroyed and the composition cures rapidly in a number of minutes to produce a silicone elastomer. Such inhibitors are used in these SiH-olefin platinum catalyzed compositions so as to enhance their pot life or working life after the two packages are mixed and prior to cure.
There also has been developed a one-component SiH-olefin platinum catalyzed silicone rubber composition in which the inhibitor is a hydroperoxy compound which is so effective that the composition can be packaged as a one package system for prolonged periods of time and yet when exposed to elevated temperatures can cure to form a silicone elastomer in a matter of minutes. Such a composition is, for instance, disclosed in the patent application of William J. Bobear, entitled "Inhibitor for Platinum Catalyzed Silicone Rubber Compositions", Ser. No. 675,377, now pending.
Such SiH-olefin platinum catalyzed compositions find great use as for the preparation of silicone molds, for paper release coatings and as encapsulants. However, while such compositions are very suitable for paper release applications and for silicone molds because of their good release properties, such silicone rubber compositions are utilized with some difficulty as encapsulants and for potting applications because of poor adherence to required bonding surfaces. For potting applications, it is often desired to pot or enclose electric circuitry with a silicone composition to protect the electric circuitry from dirt, moisture and mechanical shock. There has even been developed a clear SiH-olefin platinum catalyzed composition for such potting and encapsulating applications so that if there is a malfunction in the electric circuitry, the technician can view the circuitry through the clear potting composition to determine the corrective action to be taken.
Other relevant properties of such SiH-olefin platinum catalyzed compositions for potting and encapsulating electric circuitry are that they are non-conductive of electricity, resistant to ozone and weathering, and water reppellent. These properties make such compositions ideal encapsulant and potting materials. However, such SiH-olefin platinum catalyzed compositions still had difficulty with respect to potting and encapsulating applications. Because of their good release properties these SiH-olefin platinum catalyzed silicone rubber compositions would not adhere very well to the electric circuitry and circuitry board substrates such that a very poor bond was formed between the silicone elastomeric composition and the substrates. Accordingly, because of the formation of such poor bonds between the silicone elastomeric composition and the encapsulated substrate, the silicone elastomeric encapsulant or potting compound had a tendency to come loose from the substrate and thus not fully protect the electric circuitry from moisture, dirt and mechanical shock.
To solve this problem, primers were developed for such SiH-olefin platinum catalyzed compositions to apply them to metal substrates and specifically, electric circuitry substrates and the electric circuitry itself so that the cured silicone elastomer would adhere with good bond strength to the encapsulated and potted substrate. Such primer compositions are generally combinations of active ingredients dissolved in a volatile solvent or solvent mixture. The primer is applied to the substrate to be encapsulated or potted, say by wiping or spraying. The solvent is allowed to evaporate, leaving a surface coating more suited to bonding. The silicone rubber potting composition is applied thereover and allowed to cure to produce a silicone elastomer with a good bond between the silicone elastomer and the electric circuitry that is to be potted or encapsulated. Unfortunately, clear silicone potting compounds that employ vinyl containing silicone resins rather than fillers for reinforcement still did not adhere satisfactorily even when such primers were employed. Examples of materials that are desired for electric circuitry substrates that are to be bonded to by such SiH-olefin platinum catalyzed compositions are for instance, glass, aluminum, steel, copper and stainless steel which, of course, includes the metals of the electric circuitry itself. Accordingly, the use of such primers sometimes operated with effectiveness to bind such SiH-olefin platinum catalyzed compositions with good bond strengths to the foregoing metal substrates. However, even when they worked well there were various problems associated with primers.
First and foremost of all, it required an additional step in the preparation of the encapsulated or potted electric circuitry apparatus, that is, the application of the primer to the substrate. In addition it increased the cost of the total operation both in the labor involved to apply the primer composition to the electric circuitry substrate and also in the cost of manufacture and distribution of the primer composition itself. Further, such use of primer compositions made it necessary to set forth more detailed instructions than was usual in the preparation of the encapsulated apparatus. Accordingly, for such encapsulated and potting applications it is highly desirable to have an SiH-olefin platinum catalyzed composition which has a self-bonding additive in it such that a primer is not needed for the application of the composition to encapsulate or pot electric circuitry. It is especially highly desirable to have a clear SiH-olefin platinum catalyzed composition which has a self-bonding additive in it, such that satisfactory adherence is obtained without the use of a primer. Various attempts have been made to accomplish this but failed for one reason or another. One of the reasons why many of the additives that were added to the SiH-olefin platinum catalyzed composition did not operate properly was that the additive would poison or deactivate the platinum catalyst such that the composition would not cure upon application. Other supposed self-bonding additives were simply not effective in establishing a good bond between the cured elastomer and the substrates of interest. Silyltriallylisocyanurates were, for instance, tried as self-bonding additives for room temperature compositions but such additives did not perform as well as would be desired. Such use of the silyltriallylisocyanurates in traditional room temperature vulcanizable compositions are, for instance, set forth in Hardman and Berger, U.S. Pat. No. 3,882,083, whose disclosure is hereby incorporated by reference. Another example of such an SiH-olefin platinum catalyzed composition is to be found in Ballard U.S. Pat. No. 3,527,655. The adhesive component of this composition was the reaction product of a vinyltrichlorosilane and a vinyl trialkoxy silane. Accordingly, it was highly desirable to find a self-bonding additive for SiH-olefin platinum catalyzed compositions which would adhere such compositions with good bond strength and in the absence of a primer to such diverse substrates as glass, aluminum, steel, copper, stainless steel, so that such compositions would be desirable compositions for the encapsulation and potting of electrical circuitry.
It is one object of the present invention to provide for a self-bonding additive for SiH-olefin platinum catalyzed compositions. It is another object of the present invention to provide for a process for producing a self-bonding SiH-olefin platinum catalyzed composition. It is an additional object of the present invention to provide for a process for adhering SiH-olefin platinum catalyzed compositions to electrical circuitry substrates without the use of a primer.
It is still an additional object of the present invention to provide for an inexpensive self-bonding additive for SiH-olefin platinum catalyzed compositions.
It is still a further object of the present invention to provide for a preferred process for producing a partial hydrolysis product of an aliphatically unsaturated hydrolyzable alkoxy silane, which can be utilized as a self-bonding additive for SiH-olefin platinum catalyzed compositions.
These and other objects of the present invention are accomplished by means of the disclosure set forth hereinbelow.